Focussing on the third type of system mentioned above, different paddles designs have been proposed. For example, US-A-2008/0018113 and GB-A-2,333,130 describe downward hanging, flat, symmetric paddles that intersect the wave motion near the surface. These devices gradually absorb energy and flatten the waves as they pass beneath.
WO-A-2004/097212 and EP-A-2,292,924 are designed for shallow water with a symmetric paddle hinged about the bottom. WO-A-2004/097212 describes a substantially flat paddle with a slight vertical curvature. While the paddle in EP-A-2,292,924 is constructed from a sequence of horizontal tubular sections that give both faces a contoured vertical profile. The paddle additionally includes a pair of ‘end effectors’ that protrude evenly from each vertical side.
Though the constructions of the paddles within these devices all differ, they are mostly designed around the presumption that wave conditions driving a paddle in the direction of the energy movements (“forward”) are equivalent, though applied to the opposite paddle face, to the forces that drive it against the energy movement (“backward”). Therefore each of these designs would operate equally well if installed in reverse. However, the flow of ocean energy typically has a strong directional bias: e.g. in the northern North Sea 95% of the incoming energy arrives within an arc of +/−30° of the mean direction.
Each of these paddles also have a substantially flat face on the lee side of the paddle. Therefore, when these paddles move they dissipate a significant amount of energy through the creation of secondary waves that propagate from the paddle. In an ideal system there would be no significant waves on the lee side of the paddle. One way to achieve this is to remove the water on the lee side of the paddle and create an air gap within which the paddle can move freely. However, this is both complicated and expensive to build and would require regular maintenance of the high-pressure waterproof seals.
What is needed is a straightforward paddle design that takes advantage of the directional bias in waves, in particular ocean waves, to increase the wave energy captured, while simultaneously reducing waves generated on the lee side to maximise its overall energy absorbing properties.